1. Field of the Invention
The present invention relates to a sheet handling apparatus, and more particularly to a sheet handling apparatus for sorting and/or stapling sheets which have obtained images in a copying machine or a printer and have been ejected therefrom.
2. Description of Related Art
Conventionally, apparatuses for handling image-formed sheets, which are called finishers, have various functions, such as a function of collating sheets (sorting), a function of grouping sheets by page so that sheets in a group will have the same page (grouping), a function of stapling sheets, a function of punching sheets, etc. Meanwhile, recently, such sheet handling apparatuses have been demanded to have a large capacity. In order to make a sheet handling apparatus have a large capacity, it is required to provide a mechanism for taking sets of sheets which have been sorted and stored in bins therefrom into a large-capacity tray set by set after stapling the sheets or without stapling the sheets.
In such a sheet handling apparatus with a large-capacity tray, when a large number of stapled sets are stacked on the tray, the stack of sheet sets is very voluminous at the stapled portion. Accordingly, the number of stapled sets which can be stacked on the tray is smaller than the number of unstapled sets which can be stacked thereon. However, this point has not been considered in designing a sheet handling apparatus, and such a conventional sheet handling apparatus is likely to have trouble in stacking stapled sets of sheets on a large-capacity tray. In such a conventional apparatus, also, because the stack of stapled sets on the tray is partly voluminous at the stapled portion, the sets stapled on the tray may become out of alignment or may bend.
There has been conventionally a type of sheet handling apparatus which has a large-capacity tray above bins. In this type, the large-capacity tray is also used as a non-sort tray which receives sheets which are not required to be distributed among the bins for sorting or grouping. The large-capacity tray also receives sets of sheets which have been distributed among the bins and transported therefrom by a vertical transporting means. When the transporting means delivers a set of sheets onto the large-capacity tray, there is a possibility that the set of sheets may push a set of sheets which have been previously delivered onto the tray. Especially when unstapled sets of sheets are being stacked on the tray, it is more likely to occur that upper sheets of a previously delivered set are punched, whereby the set will be out of alignment.
When the large-capacity tray is used as a non-sort tray, the transporting means is set on a level high above the surface of the tray so as to secure sufficient capacity of the tray for sheets. However, when sets of sheets are stacked on the tray, if the transporting means is set on this level for delivery of each set to the tray, the sets of sheets may bend.
Further, when stapled sets of sheets are stacked on the tray, the stapled portion of the stack of sets is more voluminous than the other portions, and a set currently delivered to the tray may collide with the stapled portion of the stack.
Also, there has been conventionally a type of sheet handling apparatus which has a large-capacity tray below bins. In this type, each set of sheets is dropped into the tray, and the sheets may be put out of order if the sheets are not stapled. On the other hand, in the type which has a large-capacity tray above the bins and has a mechanism for handling and lifting a set of sheets to the tray, a space for the lifting of a set of sheets is necessary, thereby increasing the size of the apparatus.
Incidentally, in order to take a set of sheets out of a bin, the present inventors have decided to adopt a method wherein the set of sheets is nipped between an upper roller and a lower roller and held up from the bin. However, an upright stopper is provided for each bin at the end portion so that sheets in each bin will be put into alignment, and each stopper has a protruding portion at the end so that sheets will not fall down from each bin even with vibration due to movement of the bin. Therefore, with a mechanism which merely nips a set of sheets between an upper roller and a lower roller and holds it up, it is likely that the set of sheets hits the edge against the stopper or is caught in the protruding portion of the stopper, thereby putting the sheets out of alignment, failing in take-out of the set of sheets and/or damaging the sheets.